It is common and usual practice in sealing the top portion of rotary valves to use a top seal that seals against media leakage while simultaneously accommodating rotational movement of the valving element relative to a valve body. The valving element of a rotary valve has a closure portion which is rotatably fitted within a valve body. This closure portion of the valve is joined by a stem or shaft portion which extends out of the valve body to interact with an actuator and transmit torque to the closure portion. This torque is used to rotate the closure portion within the valve body and to open or close a passageway in the valve.
In plug valves, it is common practice to seal the top of the valve with a centrally apertured diaphragm with the shaft portion of the valve extending through the central aperture of the top seal. The mechanism for the adjustment of plug valves normally turns around the compression of two sealing parts to prevent leakage. These mechanisms involve normally a plurality of tightening bolts or screws (usually three but sometimes two).
Examples of such valves can be seen in U.S. Pat. Nos. 3,235,272 (Smith); 4,159,818 and 4,475,713 (Reed et al.).
While all of the above mentioned sealing arrangements have been highly satisfactory, they are not without their attendant disadvantages. For example, the tightening bolts or screws often need to be screwed simultaneously to prevent unwanted side loading on the system. Furthermore, these bolts or screws can be difficult to access with tools, especially in case of toxic leakage. As a result, these screws are rarely adjusted which reduces the effective life of the valve.